In C/C++ what’s the simplest way to reverse the order of bits in a byte?

by

This should work:

unsigned char reverse(unsigned char b) {
   b = (b & 0xF0) >> 4 | (b & 0x0F) << 4;
   b = (b & 0xCC) >> 2 | (b & 0x33) << 2;
   b = (b & 0xAA) >> 1 | (b & 0x55) << 1;
   return b;
}

First the left four bits are swapped with the right four bits. Then all adjacent pairs are swapped and then all adjacent single bits. This results in a reversed order.

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